Leuco triarylmethane/hexaarylbiimidazole color forming system containing a deactivator

ABSTRACT

A PHOTOIMAGABLE AND PHOTODEACTIVATABLE COMPOSITION OF (A) A SALT OF A LEUCO TRIARYLMETHANE AND A SALT-FORMING ACID; (B) A HEXAARYLBIMIDAZOLE WHICH ABSORBS PRINCIPALLY IN THE ULTRAVIOLET REGION AND IS A PHOTOXIDANT FOR THE SALT OF THE LEUCO TRIARYLMETHANE PRESENT IN AN AMOUNT OF FROM ABOUT 1 TO 2 MOLES PER MOLE OF SAID SALT OF THE LEUCO TRIARYLMETHANE; (C) 1,6-PYRENEQUINONE OR 1,8-PYRENEQUINONE OR BOTH, PRESENT IN AN AMOUNT OF FROM ABOUT .04 TO .4 MOLE PER MOLE OF HEXAARYLBIMIDAZOLE; (D) A VISIBLE LIGHT-ABSORBING CARBONYL COMPOUND SELECTED FROM 9, 10-PHENANTHRENEQUIONE, PERINAPHTHENONE, OR 4-METHOXY-1,2-NAPHTHOQUINONE; PRESENT IN AN AMOUNT OF FROM ABOUT .05 TO 2 MOLE OF HEXAARYLBIMIDAZOLE; AND (E) AN ETHER CONTAINING AT LEAST ONE OXYMETHYLENE GROUP WHEREIN THE METHYLENE BEARS AT LEAST ONE HYDROGEN; PRESENT IN AN AMOUNT PROVIDING FROM ABOUT 50 TO 500 OXYMETHYLENE GROUPS PER MOLE OF THE COMBINED QUINONE COMPONENTS (C) AND (D).

United States Patent Int. Cl. G03c 1/72 US. CI. 9690 14 Claims ABSTRACT OF THE DISCLOSURE A photoimagable and photodeactivatable composition of (A) A salt of a leuco triarylmethane and a salt-forming acid;

(B) A hexaarylbiimidazole which absorbs principally in the ultraviolet region and is a photooxidant for the salt of the leuco triarylmethane present in an amount of from about 1 to 2 moles per mole of said salt of the leuco triarylmethane;

(C) 1,6-pyrenequinone or 1,8-pyrenequinone or both, present in an amount of from about .04 to .4 mole per mole of hexaarylbiimidazole;

(D) A visible light'absorbing carbonyl compound selected from 9,IO-phenanthrenequinone, perinaphthenone, or 4-methoxy-1,2-naphthoquinone; present in an amount of from about .05 to 2 moles per mole of hexaarylbiimidazole; and

(E) An ether containing at least one oxymethylene group wherein the methylene bears at least one hydrogen; present in an amount providing from about 50 to 500 oxymethylene groups per mole of the combined quinone components (C) and (D).

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to photosensitive compositions. More particularly it is directed to an admixture of a photoactivatable color-forming system comprising a salt of a leuco triarylmethane and a hexaarylbiimidazole, and a system for photodeactivating the color-forming system comprising a mixture of selected quinones and an aliphatic ether.

(2) Description of the prior art British Pat. 1,047,569 discloses the color-forming system employed in the present invention and discloses that the leuco triarylmethane/hexaarylbiimidazole combination forms color on exposure to ultraviolet light. British Pat. 1,057,785 discloses that the leuco triarylmethane/ hexaarylbiimidazole system can be deactivated against color formation with light of a second wavelength, by incorporating therewith a light activatable oxidationreduction system which on radiation with the light of a second wavelength produces a reducing agent which reacts with the photolyzed hexaarylbiimidazole, thus preventing color formation.

One photoactivatable oxidation-reduction system disclosed by British Pat. 1,057,785 involves a visible-light activatable quinone in combination with a polyether bearing an extractable hydrogen. Irradiation of the British Pat. 1,057,785 system with ultraviolet light produces color corresponding to the dye form of the leuco triarylmethane; while irradiation with visible light deactivates the color-forming components against color formation. The deactivaton of the color-forming components is attributable to in situ hydroquinone formation from the quinone employed, which then reacts with the photolyzed hexaarylbiimidazole.

Since the hexaarylbiimidazloes can absorb at wavelengths as high as 430 m which are the violet wavelengths, the compositions of British Pat. 1,057,785, tend to form some color when irradiated with the deactivating visible light radiation. Since color formation is ordinarily undesirable during the deactivating step, it is suppressed by controllng the deactivating conditions. A filter can be employed to screen activating radiation from the colorforming components; a monochromatic light can be employed that only the deactivating components can absorb; or a light source can be employed which emits principally in the photodeactivation region with substantially no light emitted in the region of hexaarylbiimidazole absorption.

However, in some applications it is desirable to eliminate the need for deactivating under controlled conditions. This can be accomplished by providing for rapid photodeactivation, i.e., by employing deactivation components which react to deactivate so rapidly that the competing color-formation reaction cannot get underway. By employing such components, color formation can be prevented from occurring upon exposure of the system to light such as sunlight, roomlight or daylight, which contains intense violet wavelengths.

US. Pat. 3,390,994, issued July 2, 1968, describes a rapidly photodeactivatable system for use with the leuco triarylmethane/hexaaiylbiimidazole color-forming components which employs either pyrenequinone or phenanthrenequinone as the oxidant member of the deactivating system and an alkyl nitrilotriacetate or alkyl nitrilotripropionate as the reductant member. Although this system possesses rapid deactivation properties, it tends to form color rather slowly and tends to be limited in its maximum color attainment. Moreover, it is sensitive to human handling. When coatings of it are touched prior to irradiation for color formation, these touched areas are not imaged and appear as uncolored fingerprint areas after the coating is subsequently irradiated with colorforming irradiation.

It is an object of this invention to provide photosensitive compositions which form color rapidly, which attain maximum color, and which are not sensitive to fingerprinting. These and other objects of the invention Will become apparent hereinbelow.

SUMMARY OF THE INVENTION The photosensitive compositions of this invention comprise an intimate admixture of (A) A salt of a leuco triarylmethane and a salt-forming acid;

(B) A hexaarylbiimidazole which absorbs principally in the ultraviolet region and is a photooxidant for the salt of the leuco triarylmethane present in an amount of from about 1 to 2 moles per mole of said salt of the leuco triarylmethane;

(C) 1,6-pyrenequinone or 1,8-pyrenequinone or both, present in an amount of from about 0.04 to 0.4 mole (preferably 0.1 to 0.3 mole) per mole of hexaarylbiimidazole;

(D) A visible light-absorbing carbonyl compound selected from 9,IO-phenanthrenequinone, perinaphthenone, or 4-methoxy-1,2-naphthoquinone; present in an amount of from about 0.05 to 2 moles (preferably 0.15 to 0.75 mole) per mole of hexaarylbiimidazole; and

(E) An ether containing at least one oxymethylene group wherein the methylene bears at least one hydrogen; present in an amount providing from about 50 to 500 oxymethylene groups per mole of the combined quinone components (C) and (D).

DESCRIPTION OF THE INVENTION In the foregoing definition, components (A) and (B) comprise the color-forming system; while components (C), (D), and (E) comprise the deactivating system The mixture of the quinones of components (C) and (D) with the ether of (E) are critical in achieving the objects of the invention. Use of a single quinone, or any other quinone mixture, or other reductants in place of the ether of (E) fail to result in providing the properties that characterize the invention, particularly, the sunlight, roomlight, or daylight color-formation resistance and the absence of fingerprinting.

(1) THE DEACT'IVATING SYSTEM The deactivating components (C), (D) and (E) comprise an oxidation-reduction system which, upon exposure to visible light, react to form a product which deactivates the hexaarylbiimidazole (B). The oxidant member of the deactivating oxidation-reduction system is a mixture of at least two compounds (one from (C) and one from (D) which absorb light in the 400 to 500 my region. Preferably, component (C) is a mixture of both 1,6-pyrenequinone and 1,8-pyrenequinone in molar proportions ranging from 70:30 to 30:70. Preferably, also (D) is 9,10-phenanthrenequinone in an amount of from about 1 to 10 moles per mole of (C) and most preferably in an amount of 1.5 to 2.5 moles/per mole of (C); and the mixture of (C) and (D) is 0.1 to 0.2 moles (preferably 0.2 to 1 mole) per mole of (B).

The reductant member of the deactivating oxidationreduction system is the ether defined in (E). For practicality, it should be substantially non-volatile (boiling at 100 C. and above) and serve to solubilize or plasticize the leuco triarylrnethane/hexaarylbiimidazole/mixed quinone composition so as to provide flexible substantially homogeneous coating compositions and to facilitate both the color-forming and the color-preventing reactions. Suitable reductant members include polyethers containing aliphatic polyether linkages, such as ethyleneoxy or propyleneoxy linkages. These may be represented by the formula where n is an integer from 0 to l; m is an integer from 1 to 15; R is hydrogen, alkyl, phenyl, alkylphenyl, biphenylyl or acyl; R is hydrogen when n is zero and is hydrogen, hydroxy or OR when n is 1. Preferably the alkyl and acyl radicals each contain from 1 to 18 carbon atoms. Most preferably, these reductant members have the formula RO(CH CH O) H where m is as above and R is phenyl, alkylphenyl or biphenylyl.

Representative and preferred classes are the polyethylene glycols such as the commercially available Carbo- Waxes; the analogous polypropylene glycols; and related materials such as phenol-ethylene oxide adducts, for example the ethers and polyethers obtained by reaction of ethylene oxide with o-, m-, p-cresol, 0-, m-, and p-phenylphenol and with p-nonylphenol, including such commercially available materials as the Igepal alkylphenoxy polyoxyethylene ethanols. Still others are the acetates, propionates, butyrates and other carboxylate esters of the above hydroxy-terminated polyalkyleneoxides and of aliphatic polyols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, and glycerol.

Representative materials are additionally described in the examples.

(2) THE IMAGING SYSTEM The salt of a leuco triarylmethane is derived from an aminotriarylmethane and a salt-forming acid. Preferably the aminotriarylmethane is one wherein at least two of the aryl groups are phenyl groups having (a) an R R N- substituent in the position para to the bond to the methane carbon atom wherein R and R are each groups selected from hydrogen, C to C alkyl, Z-hydroxyethyl, Z-cyanoethyl, benzyl or phenyl, and (b) a group ortho to the bond to the methane carbon atom which is selected from lower alkyl, lower alkoxy, fluorine, chlorine, bromine, or butadienylene which when joined to the phenyl group forms Y Y Ill I RiR=N(!]NRiR4 X wherein R and R are selected from lower alkyl (preferably ethyl) or benzyl, Y and Y are lower alkyl (preferably methyl) and X is selected from p-methoxyphenyl, Z-thienyl, phenyl, l-naphthyl, 2,3-dimethoxy-phenyl, 3-4-methylenedioxyphenyl, or p-benzylthiophenyl. Preferably X is selected from phenyl, l-naphthyl, or p-benzylthiophenyl.

These triarylmethanes are employed as salts of strong acids: for example, mineral acids such as hydrochloric, hydrobromic, sulfuric, nitric, phosphoric; organic acids such as acetic, oxalic, p-toluenesulfonic, trichloroacetic acid, trifluoroacetic acid, perfiuoroheptanoic acid; and Lewis acid such as zinc chloride, zinc bromide, and ferric chloride; the proportion of acid usually varying from 0.33 mole to 1 mole per amino group. The term strong acid as used herein is defined as an acid which forms a salt with an anilino amino group.

Specific examples of the aminotriarylmethanes employed in this invention are:

bis(4-amino-2-butylphenyl) (p-dirnethylaminophenyl) methane bis(4-amino-2-chlorophenyl) (p-aminophenyl methane bis(4-amino-3-chlorophenyl) (o-chlorophenyl)methane bis(4-amino-3-chlorophenyl)phenylmethane bis (4-amino-3,5-diethylphenyl) (o-chlorophenyl) methane bis(4-amino-3,S-diethylphenyl) (o-ethoxphenyl) methane bis(4-amino-3,S-diethylphenyl) (p-methoxyphenyl) methane bis(4-amino-3,5-diethylphenyl)phenylmethane bis 4-amino-3-ethylphenyl) (o-chlorophenyl) methane bis p-aminophenyl) (4-amino-m-tolyl methane bis (p-aminophenyl) (o-chlorophenyl )methane bis (p-aminophenyl) (p-chlorophenyl) methane bis(p-aminophenyl) (2,4-dichlorophenyl)methane bis (p-aminophenyl) (2,5-dichlorophenyl)methane bis(p-aminophenyl) (2,6-dichlorophenyl)methane bis (p-aminophenyl)phenylmcthane bis (4-amino-o-tolyl) (p-chlorophenyl )methane bis(4-amino-o-tolyl) (2,4-dichlorophenyl)methane bis (p-anilinophenyl) (4-amino-m-tolyl)methane bis (4-benzylamino-2-cyanophenyl) (p-aminophenyl) methane bis (p-benzylethylaminophenyl) (p-chlorophenyl) methane bis (p-benzylethylaminophenyl) (p-die thylaminophenyl) methane bis(4-diethylamino-o-tolyl) (2-diethylamino-4-methyl-5- thiazolyl methane bis(4-diethylamino-o-tolyl) (2-diethylamino-5-methyl-6- benzoxazolyl methane bis(4-diethylamino-o-tolyl) (Z-cliethylamino-S-rnethyl-fibenzothiazolyl methane bis 4-diethylamino-o-tolyl) (l-ethyl-2-methyl-3-indolyl) methane bis(4-diethylamino-o-tolyl) (l-benzyl-2-methyl-3-ind0lyl) methane bis(4-diethylamino-o-tolyl) (l-ethyl-2-methyl-5-methoxy1- 3 -indolyl methane bis(1-o-xylyl-2-methyl-3 -indolyl) (4-diethylamino-o-tolyl) methane bis (4-diethylamino-o-tolyl) l-ethyl-S-indolinyl methane bis( 1-isobutyl-6-methyl-S-indolinyl) (4-diethylamino-otolyl methane bis(4-diethylamino-o-tolyl) (8-methyl-9-julolindinyl) methane bis(4-diethylamino-2-acetamidophenyl) 4-diethylaminoo-tolyl methane 4- [bis (4-diethylamino-o-tolyl methyl -N-ethylacetanilide bis[4-(1-phenyl-2,3-dimethyl-5-pyrazolinyl) (4-diethy1- amino-o-tolyl )methane bis(4-diethylamino-o-tolyl) (7-diethylamin0-4-methyl-3- coumarinyl methane bis (4-diethylamino-o-tolyl) (4-acrylamidophenyl) methane bis (4-diethylamino-o-tolyl) p-benzylthiophenyl methane bis 4-diethylamino-o-tolyl) (4-isopropylthio-3-methylphenyl methane bis(4-diethylamino-o-tolyl) (4-chlorobenzy1thiopheny1) methane bis(4-diethylamino-o-tolyl) (2-fury1)methane bis 4-dieth ylamino-o-tolyl) 3 ,4-methylenedioxyphenyl) methane bis 4-diethylamino-o-to1yl) (3,4-dimethoxyphenyl) methane bis(4-diethylamino-o-tolyl) (3-methyl-2-thienyl)methane bis(4-diethylamino-o-tolyl) (2,4-dimethoxyphenyl) methane bis [4-( Z-cyanoethyl) (Z-hydroxyethyl)amino-o-tolyl] p-benzylthiophenyl) methane bisl4-(2-cyanoethy1) (Z-hydroxyethyl) amino-o-tolyl] -2- thienylmethane bis 4-dibutyl amino-o-tolyl Z-thienylmethane bis 4-diethylamino-Z-ethylphenyl) (3,4-methylenedioxyphenyl methane bis 4-diethylamino-Z-fluorophenyl) p-benzylthiophenyl) methane bis 4-diethylamino-Z-fiuorophenyl) (3,4-methy1enedioxyphenyl) methane bis 4-diethylamino-o-tolyl) p-methylthiophenyl )methane bis 4-diethylamino-o-tolyl Z-thienylmethane bis(4-dimethylamino-2-hexylphenyl) (p-butylthiophenyl) methane bis[4-(N-ethylanilino)-o-tolyl] (3,4-dibutoxypheny1) methane bis [4-bis 2-hydroxyethyl amino-Z-fluorophenyl] p-benzylthiophenyl)methane bis(4-diethylamino-o-tolyl)-p-chlorophenyl methane bis(4-diethylamino-o-tolyl)-p-bromophenyl methane bis(4-diethylamino-o-tolyl)-p-fiuorophenyl methane bi s 4-diethylamino-o-tolyl -p-tolyl methane bis 4-diethylamino-o-tolyl) -4-methoxyl-naphthyl methane bis 4-diethylamino-o-tolyl -3 ,4,5-trimethoxyphenyl methane bis(4-diethylamino-o-tolyl)-p-hydroxyphenyl methane bis 4-diethylamino-o-tolyl -3-methylthienyl methane The hexaarylbiimidazoles are the 2,2,4,4,5,5'-hexaarylbiimidazoles (sometimes referred to as 2,4,5-triarylimidazolyl dimers) that are dissociable to the corresponding triarylimidazolyl radicals wherein the aryl groups may be the same or cliflferent, carbocyclic or heterocyclic subtituent free or bearing substituents that do not interfer with the dissociation step and he subsequent oxidation of the leuco aminotriarylmethane.

The hexaarylbiimidazoles can be represented as the dimers of 2,4,5-triarylimidazolyls of the formula wherein A, B, and D are aryl radicals, as previously defined.

The hexaarylbiimidazoles can also be represented by the formula wherein A, B and D stand for aryl radicals described above. In these dimers each imidazolyl ring has two conjugated double bonds and a single bond joining the two rings. Upon dissociation, the dimer forms the corresponding 2,4,5-triarylimidazolyl radical. The B and D groups can normally carry 0-3 substituents, the A group 0-4 substituents.

The aryl groups include oneand two-ring aryls, such as phenyl, biphenyl, naphthyl, pyridyl, furyl and thienyl. Suitable inert substituents on the aryl groups have Hammett sigma (para) values in the -.5 to 0.8 range and are other than hydroxyl, sulfhydryl, amino, alkylamino or dialkylamino. Preferably, these inert substituents are free of Zerewitinolf hydrogen, i.e., have no hydrogens reactive towards methyl magnesium iodide. Representative substituents and their sigma values (relative to H=.00-), as given by Jaffe, Chem. Rev. 53, 219-233 (1953) are: methyl (0.17), ethyl (-0.15), t-butyl (0.20), Phenyl (0.01), butoxy (0.32), phenoxy (0.03), fluoro (0.06), chloro (0.23), bromo (0.23), iodo (0.28), methylthio -0.05), nitro (0.78), ethoxycarbonyl (0.52), and cyano (0.63). The foregoing substituents are preferred; however, other substituents which may be employed include trifluoromethyl (0.55), chloromethyl (0.18), carboxyl (0.27), cyanomethyl (0.01), 2-carboxyethyl (0.07), and methylsulfonyl (0.73). Thus, the substituents may be halogen, cyano, lower hyldrocarbyl (including alkyl, halo alkyl, cyanoalkyl, hydroxyalkyl and aryl), lower alkoxy, aryloxy, lower alkylthio, arylthio, sulfo, alkyl sulfonyl, arylsulfonyl, and nitro, and lower alkylcarbonyl. In the foregoing list, alkyl groups referred to therein are preferably of 1-6 carbon atoms; while aryl groups referred to therein are preferably of 6-10 carbon atoms.

Preferably the aryl radicals are carbocyclic, particularly phenyl, and the substituents have Hammett sigma values in the range -.4 to +.4, particularly lower alkyl, lower alkoxy, chloro, fluoro, bromo and benzo groups.

In a preferred biimidazole class, the 2 and 2' aryl groups are phenyl rings bearing an ortho substituent having a Hammett sigma value in the range -.4 to +4. Preferred ortho substituents are fluorine, chlorine, bromine, methyl and methoxy groups, especially chloro. Such dimers tend less than other dimers to form color when the light-sensitive compositions are applied to and dried on substrates at somewhat elevated temperatures, e.g. in the range 70- C.

GROUPS THAN PHENYL IN IMIDAZ- OLYL RADICAL II.-OTHER RIN G 2-poslti0n 4-positlon fi-position 2,4-d1pentylphenyl. Z-naphthyl 2nuphtliyl. p-Mcthoxyphcnyl ..do D0. o-Methoxycarbonyl phony] do Phenyl. (l-methoxy-Z- naphthyl) Phcnyl Do. (3-methoxy-2- naphthyl ..do Do. l-naphthyl do Do. o-Pentyloxycarbonyl phenyl 2-naphthyl 2-naphthyl. 3-pyridyl Phenyl Phenyl.

The above dimers of 2,4,5-triarylimidazolyl radicals which provide light-activated components for the invention compositions are characterized by the property of dissociating into two triarylimidazolyl free radicals when illuminated with ultraviolet light of a wavelength from about 2000 A. to 4200 A. Such a dissociation may be detected, and the existence of the free radicals discerned, by electron paramagnetic resonance, by ultraviolet spectra, and by visible spectra.

(3) OTHER COMPONENTS Inert solvents are usually employed to dissolve the components of the composition of this invention and to provide a fluid medium for convenient application of the light-sensitive composition to substrates. To obtain the final coated article the solvent is normally removed as, e.g., by evaporation. It is often beneficial to leave a small residue of solvent in the dried composition so that the desired degree of imaging can be obtained upon subsequent irradiation. Ordinary drying such as that employed in paper manufacture or in film casting results in the retention of ample solvent to give a composition with good photosensitivtiy. The compositions so produced are dry to the touch and stable to storage at room temperature. Indeed, moisture of the air is absorbed by many of the compositions, particularly those comprising an acid salt of an amino leuco form of a dye on cellulosic substrates, and serves as a suitable solvent.

In general, suitable solvents have boiling points of at least 40 C. at atmospheric pressure, although solvents with higher boiling points may be used. Examples are amides such as N,N-dimethylformamide and N,N-dimethylacetamide; alcohols and ether alcohols such as methanol, ethanol, l-propanol, 2-propanol, butanol, and ethylene glycol; esters such as methyl acetate and ethyl acetate; aromatics such as benzene, o-dichlorobenzene, toluene; ketones such as acetones, methyl ethyl ketone, S-pentanone; aliphatic halo carbons such as methylene chloride, chloroform, 1,1,2-trichloroethane, l,l,2,2-tetrachloroethane, 1,1,2-trichloroethylene; miscellaneous solvents such as dimethylsulfoxide, pyridine, tetrahydrofuran, dioxane, dicyanocyclobutane, l-methyl-Z-oxohexamethyleneimine; and mixtures of these solvents in various proportions may be required to attain solution of the color forming and color preventing compounds.

Polymeric binders may also be present in the lightsensitive compositions to thicken them or adhere them to substrates. Binders can also serve as a matrix for the color-forming composition and the mixture may be cast, extruded or otherwise formed into unsupported imageable films. Light-transparent and film-forming polymers, are preferred. Examples are ethyl cellulose, polyvinyl alcohol, polyvinyl chloride, polystyrene, polyvinyl acetate, poly(methyl methacrylate), cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, chlorinated rubber, copolymers of the above vinyl monomers, and gelatin. Binder or matrix amounts vary from about 0.5 part to about 200 parts by weight per part of combined weight of the leuco triarylmethane and the hexaarylbiimidazole. In general from 0.5 to parts are used as adhesive or thickener, while higher amounts are used to form the unsupported films. With certain polymers, it may be desirable to add a plasticizer to give flexibility to the film or coating. As noted above the preferred classes of methyleneoxy hydrogen donors described above as reductants in the deactivation system also serve as plasticizers. Other plasticizers that may be used are the alkyl phthalates and phosphates, such as dimethyl phthalate, diethyl phthalate, dioctyl phthalate, tributyl phosphate, trihexyl phosphate, triooctyl phosphate, triphenyl phosphate, tricresyl phosphate and cresyl diphenyl phosphate.

(4) PREPARATION OF THE COMPOSITIONS A common procedure is to make a solution of a leuco triarylmethane defined as in (A) in the summary above ranging in concentration from about 0.5% by weight to the limit of the solubility of the compounds in a solvent comprising, for instance, 50:50 by volume of N,N-dimethyltormamide and benzene, and to add to this solution, in amounts set forth further above, the hexaarylbiimidazole defined as in (B), the quinones defined as in (C) and (D) and the ether reductant defined as in (E) and optionally a binder as described above. The selection of the leuco triarylmethane will depend upon the color and quality of the image desired. Two or more leuco triarylmethanes may be used in combination to obtain a particular color or shade of color or to provide a neutral gray or black coloration in the image.

(5) SUBSTRATES In use, the compositions of this invention are usually coated upon or impregnated in substrates. The substrates are materials commonly used in the graphic arts and in decorative applications and include paper ranging from tissue paper to heavy cardboard; films of plastics and polymeric materials such as regenerated cellulose, cellulose acetate, cellulose nitrate, polyester of glycol and terephthalic acid, vinyl polymers and copolymers, polyethylene, polyvinylacetate, polymethyl methacrylate polyvinylchloride; textile fabrics; glass, wood and metals. Opaque as well as transparent substrates can be used. Substrates in which the photosensitive components are dissolved or which bear the photosensitive components as a coating on the reverse side of the substrate, i.e., on the side away from the ultraviolet light source used for image formation, must be transparent not only in the visible region but transparent to a portion of the ultraviolet range useful for image formation. The substrates must also be inert to the photosensitive materials and preferably should not dissolve the active components but absorb them and retain sufiicient solvent to provide a medium for rapid image formation upon irradiation.

In applying a solution to paper, films, fabrics, or to the surface of rigid substrates such as glass, wood or metals the solution may be sprayed, brushed, applied by a roller or an immersion coater, flowed over the surface, picked up by immersion or spread by other means. Complete coverage of the substrate may be attained or a pattern of the light-sensitive composition may be printed on the substrate. In impregnating paper, for instance, such concentrations of solution and pick-up by the paper are made so as to provide from about 0.01 mg/in. to about 5.0 mg./in. of the triarylmethane and equivalent amount of the hexaarylbiimidazole. Images of greater and lesser intensity of color are provided by the application of greater and lesser amounts of the triarylmethane to the substrate. For coating roll papers and films there may be used such typical devices for continuously laying down wet films as nip fed three roll reverse roll coating heads, gravure coaters, trailing blade coaters and Mayer bar coating heads (wherein the coating thickness is controlled by a threaded or a wire wound bar). The wet thickness is adjusted such that the dry thickness after solvent removal is in the desired range (about 0.1l.5 mils, usually around 0.3-0.5 mil on paper, 0.8-1.1 mils on film).

The substrates bearing a solution of the compositions of this invention may be dried simply at room temperature. They also may be dried under vacuum at room temperature by forced air solvent evaporation, or at elevated temperatures, as by radiant heating. The upper temperature limit is important in combination with exposure time. A short exposure to heat of 90 C. may not be detectably harmful, while several hours exposure to this heat may reduce the light sensitivity of the composition.

(6) LIGHT SOURCES, IMAGE FORMATION AND DEACTIVATION Any covnenient source of ultraviolet light may be used to activate the color-forming system to induce the formation of an image, whereas convenient sources of visible light may be used to achieve deactivation. In general, light sources that supply radiation in the region between about 2000 A. and about 4200 A. are useful in producing images with the leuco triarylmethane/hexaarylbiimidazole compositions on numerous substrates. Light sources generating radiation in the region between about 4200 A. and about 5500 A. are useful to achieve deactivation. Among the light sources which have been employed are sunlamps, pulsed and continuous Xenon flash lamps, germicidal lamps, ultraviolet lamps providing specifically light of short wavelength (2537 A.) and lamps providing light of longer wavelengths, narrow or broad band, centered near 3600 A., 4200 A., 4500 A., or 5000 A., such as fluorescent lamps, mercury, metal additive and are lamps. The light exposure time will vary from a fraction of a second to several minutes, depending upon the intensity and spectral energy distribution of the light, its distance from the composition, the nature and amount of the composition available, and the intensity of color in the image desired. There may also be used coherent light beams, for example, pulsed nitrogen lasers, argonion lasers and ionized neon lasers, whose emissions fall within or overlap the ultraviolet absorption bands of the hexaarylbiimidazole or visible absorption bands of the quinones.

Ultraviolet or visible emitting cathode ray tubes widely useful in printout systems for writing on photosensitive materials are also useful for imaging the subject compositions. These in general involve a UV- or visible-emitting phosphor internal coating as the means for converting electrical energy to light energy and a fiber optic face plate as the means for directing the radiation to the photosensitive target. For purposes of this invention, the phosphors should emit strongly below 420 m (4200 A.) so as to substantially overlap the near UV-absorp tion characteristic or between about 420 m to about 550 m to overlap the visible absorption characteristics of the novel imaging compositions. Representative phosphors include the P4B (emitting at 300550 m peaking at 410 m P16 (330-460 m peaking at 380 me) and P22B (3905l0 ma, peaking at 450 my) types. Other phosphors which may be used are the P11 (400-560 m peaking at 460 my.) and ZrP O types. (The Electronic Industries Association, New York, N.Y., assigns P-numbers and provides characterizing information on the phosphors; phosphors with the same P-number have substantially identical characteristics.)

Of course, it is to be understood that sources emitting principally in the ultraviolet will be most effective for activation. In instances where a light source emits strongly in both regions, optical filters 'will be required to both eliminate the visible components for effective color formation and to permit deactivation without undesired color formation.

Images may be formed by a beam of light or by exposure to light of a selected area behind a negative, a stencil, or other relatively opaque pattern. The negative may be a silver negative with cellulose acetate or polyester film. The negative may also be one in which the opacity results from aggregations of areas of different refractive index. Image formation may also be accomplished in conventional diazo printing apparatus, or in a thermography device, provided the instrument emits some of its light in the ultraviolet range. A piece of onionskin paper which bears typewriting, for example, will serve as a master pattern from which copies can be made.

The subject compositions are also activatable for the purposes of this invention by electron beams. The optimum conditions depend on the formulation and its thickness, the electron beam energy and the exposure time, and are readily determined by trial. Beams having average electron energies as low as about 10 kilovolts and as high as about 2 million electron volts have been used successfully.

The deactivating radiation employed is visible light radiation. A notable feature of this invention is that no other deactivating conditions are necessary. Thus no special precautions need be taken to prevent concurrent imaging under ambient light conditions. Negative images stable to ambient light are obtained by imagewise exposing the composition to ultraviolet light. Positive images are obtained by first imagewise exposing the composition to visible light until the desired degree of deactivation in the exposed area is attained, followed by developing the resulting latent image by exposing the composition to ultraviolet light.

(7) USEFULNESS The novel compositions of this invention are useful in such diverse fields as optical printing and imagerecording, generally, dyeing of textiles and other materials, photography, thermography and pattern layout. The compositions are also useful to sense thresholds of light, heat, pressure and combinations thereof, through the color changes they undergo when activated by such stimuli. Some specific uses are:

(1) Radiation dosimeters.-There compositions may be used as papers to determine easily the quantity of solar radiation that falls on a particular surface. It may also be useful to employ these as low cost light-meters in photographic applications. For these uses, it is necessary to compare areas which have been exposed to previously calibrated papers or surfaces, in order to allow easy analysis of the degree of radiation.

(2) Blue prints.These light-sensitive compositions can fined application in diazo printout equipment, where they can be made to give readily a variety of shades, with different speeds and sensitivities. It is possible to utilize these materials with caution in ordinary room light, rather than have to handle them in the dark.

(3) Printing applications.This invention is particularly useful for light-actuated colored image formation and provides a dry, non-silver photographic process capable of imaging in various colors and shades on various substrates, including fabrics, paper and similar fibrous sheet material. Apparatus useful in conducting photographic dye-printing is described in US. Pats. 2,214,365 and 2,655,802. Even very soft paper, as for example tissue paper, which has been treated with a composition of this invention can be readily printed by projecting the desired graphic pattern onto the treated paper and irradiating it to effect i the color-forming oxidation reaction. Subsequently, the image is fixed as described heretofore. These soft tissue paper compositions cannot be readily imaged by conventional printing techniques.

In general the compositions of this invention are broadly useful for optical printing and anywhere it is desirable to capture images as in photography, patternmaking, reproducing written, printed, drawn or typed matter, and recording radiation signals as line graphics, alpha-numerics or other characters. The applied radiation can be passed through stencils, negatives or transparencies including halftone and continuous tone negatives and positives in contact with or projected onto the composition; or, it can be reflected for impingement on the composition from printed or typed copy or objects that are opaque or transmit radiation poorly. Similarly, images of objects having areas differing in absorption and transmission characteristics are captured by placing the objects between the color forming radiation source and the composition, e.g., foot images can be recorded for fitting shoes. Multiple copies can be made using a single imaging exposure by stacking radiation-transparent assemblies comprising the composition coated on a transparent substrate such as UV-transparent film, paper or glass.

In imaging applications, the ultimately desired dye optical density pattern can be constructed stepwise, according to one or more patterns, by exposing previously unexposed areas to suitable activating radiation and/or by reexposing previously under exposed areas (i.e., areas wherein the maximum obtainable optical density has not yet been fully developed) to one or more additional exposures. Such add on capability and versatility of the invention compositions is particularly useful in recording information and creating electronically generated displays and graphics. Because the recorded images have excellent resolution on paper and film, they are suitable for microimaging for data storage. Information stored on such microfilms can be printed out on other microfilms, if desired.

The following examples illustrate the invention in greater detail.

Example 1 A coating composition was prepared by mixing the following:

Hi2 methyleneoxy groups/mole quinone mixture.

The solution was applied to bleached-sulfite roll stock paper and the acetone allowed to evaporate to give a coating about 0.4 mil thick. The coated composition rapidly developed a deep blue color when exposed to ultraviolet light, for example, on contact flashing with a Xenon flash lamp (HiCo Lite, emitting UV and visible light and approximating unfiltered sunlight) through a Corning 7-54 filter which cuts off wavelengths above 420 mu.

This composition can be completely deactivated against UV-induced color formation by irradiation with 4360 A. light using a Bausch and Lomb monochromator and an Osram HBO ZOO-watt mercury lamp at an intensity of 15- milliwatts per square centimeter of exposed surface for 70 seconds.

The marked deactivation capability of this formulation under various ambient lighting conditions, that is, its resistance to develop unwanted color under room light, daylight and sunlight conditions is illustrated with the following stability tests:

Roomlight-24 hour exposure to light from a cool white fluoroescent lamp at 50 foot candles.

Daylight-l minute exposure to sky illumination at midmorning in winter with the photosensitive surface perpendicular to the ground and facing southwest at a location of about 34 north and about 77 west at about sea level.

Sunlight-1 minute exposure to direct sunlight at midafternoon in winter with the photosensitive surface perpendicular to the ground and facing southwest at the same location as for the daylight test.

The results are tabulated below along with results obtained with formulations representative of the prior art. For these comparisons, coated papers were prepared as described above except that mixed quinones employed in the formulation set forth above were replaced by the quinones as set forth immediately below:

Increase in optical density over The data show (1) The invention composition is sufficiently stable to ambient light conditions so as not to require irradiation under controlled conditions for deactivation (image fixing).

(2) Neither the pyrenequinones alone nor the phenanthrenequinone alone provide for satisfactory daylight and sunlight stability particularly against the relatively long direct daylight exposure with its relatively high proportion of UV radiation.

(3) The mixed quinones of the invention provide for an aesthetically more appealing background color (buff versus yellow buff).

It should be noted that it is not practical to improve the stability of the prior art type formulation by increasing the proportion of either the pyrenequinone or the phenanthrenequinone since (a) large amounts of the pyrenequinones cause precipitation in storage, and (b) larger amounts of the phenanthrenequinones tend to decrease the imaging speed and the color developing capability of the system.

Example 2 A photodeactivatable photoimaging composition is prepared as in Example 1 except that the quinone mixture contains.

(a) 0.08 millimole of an approx. 1:1 mixture of 1,6-

and 1,8-pyrenequinone and (b) 0.08 millimole of 9,10-phenanthrenequinone.

This composition is identical to a control composition in its color forming speed and in the amount of color developed on exposure to ultraviolet light (the control being essentially the same composition except that it contains .16 millimole of the pyrenequinones and no phenanthrenequinone). Like the control, this example composition is deactivated completely when exposed to 4360 A. light at 15 mw./cm. intensity for 70 seconds. It is significantly more stable than the control in storage, showing a substantially lesser tendency to form precipitates. Moreover it is significantly more stable against color formation by direct daylight and sunlight exposure, giving lighter and less colored background than the control.

Examples 3 and 4 Example 1 was repeated with pyrenequinone (as the 1,6- and 1,8- approx. equimolar mixture) in combination with another quinone that can be employed in the compositions of this invention as identified below replacing the 9,10-phenanthrenequinone. The results are tabulated below in terms of the daylight and sunlight stability of the coated compositions; and are compared with compositions employing quinones in place of 9,10-phenan- 17 threnequinone that do not fall within the scope of this invention:

Increase in optical density after exposure to The compositions of Examples 3 and 4 are remarkably stable to sunlight (relatively rich in visible light) though they are less stable to prolonged direct daylight exposure (relatively rich in ultraviolet) than is the Example 1 composition also containing 9,l-phenanthrenequinone as a photooxidant component.

Example 5 A coated substrate was prepared essentially as described in Example 1 except that the quantity of acetone was increased to 61 parts in the coating formulation and the composition was coated on Mylar polyester film to give a coating 0.7 to 0.8 mil thick.

The coated film showed good imaging (blue color forming) characteristics on exposure to ultraviolet light. It developed an optical density of only 0.18 (buff color) in the daylight stability test compared to 0.61 (blue) for the same coated film containing the pyrenequinones but no phenanthrenequinone.

Example 6 Substantially similar results are obtained on increasing the 2-(o-chlorophenyl)-4,5-(m-rnethoxyphenyl)imidazolyl dimer concentration from 0.8 to 1.6 millimoles in the above invention composition of Example 5.

Examples 7-18 Photodeactivatable photoimaging compositions having improved roomlight, daylight and sunlight stability against unwanted color formation are prepared as in Example 1 except that the p-nonylphenol/ ethylene oxide adduct used as the reductant for the quinone mixture is replaced by an equal weight of an abstractable-hydrogen source containing one or more groups as identified below where R=H or CH Number of Reductant for pyrenequinone and groups per phenanthreueq uinone mole Q,

Example:

7, p-Phenylphenol/5.9 ethylene oxide adduct 230 8. o-Phenylphenol/2.25 ethylene oxide 134 adduct. 9 p-Cresol/LB ethylene oxide adduct 144 10- p-Cresol/2.25 ethylene oxide adduct 180 11 p-Cresol/3.0 ethylene oxide adduct 208 12 p-Cresol/2.0, 1,2-propylene oxide adduct 150 13 p-Cresol/LQB ethylene oxide/2.0 propylene 194 oxide adduct. 14 pCresol/3 ethylene oxide adduct acetate 176 15- p-Cresolfli ethylene oxide adduct 168 propionate. 1G. Triethylene glycol dipropionate 192 17 -[2-butoxyethoxylethyl acetate 204 18. Dipropionin (glycerol dipropionate) 122 1 Adduct signifies the alkylene ether product of the reaction of the phieinol with 5.9 (or otherwise indicated) molar proportions oi ethylene ox e.

2 The terminal hydroxy group of the adduct has been esteriiled with the indicated acyl group.

18 Example 19 Coated paper was prepared as in Example 1 except that the coating formulation contained the following leuco dyes in place of the tris(p-diethylamino-o-tolyl) methane of Example 1: 0.3323 part of bis(p-diethylamino-o-tolyl) (3,4-dimethoxyphenyl)methane and 0.0898 part of bis(pdiethylamino-o-tolyl) (p-chlorophenyl) methane.

This formulation on exposure to ultraviolet light afforded pleasing gray to black images. Like the invention formulation of Example 1, it showed good roomlight, daylight and sunlight stability. Also it was markedly superior in its photodeactivation capability to the comparable formulation containing either the pyrenequinone or the phenanthrenequinone component.

Example 20 A coated paper prepared as in Example 1 was tested for resistance to fingerprinting against another coated paper representative of the photosensitive materials described in US. Pat. 3,390,994. The coating composition of said patent contained acetone (46 parts), cellulose acetate butyrate (6 parts), the nonylphenol/ethyleneoxide adduct of Example 1 (3 parts), the biimidazole (.209 part) and leuco dye (.045 part) of Example 1, p-toluenesulfonic acid monohydrate (.200 part), pyrenequinone 1:1 mixture of 1,6- and 1,8-isomers, .0302 part), and trimethyl nitrilotripropionate (.600 part) as the primary reductant for the quinone.

The fingerprinting test was conducted by touching the coated surface of each paper with a finger tip. The paper was then placed in an envelope, which was sealed, and stored in the dark. After 24 hours the paper was removed from the envelope and exposed to ultraviolet radiation for color development.

The paper coated with the composition of this invention showed uniform color development over the entire light struck area with no sign of a fingerprint. In contrast, the control composition clearly showed in the light struck area a substantially uncolored fingerprint where the coating had originally been touched.

Remarkably similar fingerprinting results are obtained when the paper substrate is finger-touched before the photosensitive coating is applied and the procedure is repeated.

Substantially the same fingerprintin results are obtained when a mixture of phenanthrenequinone and the pyrenequinones are employed in the above control formulation, indicating that the absence of the nitrilotripropionate component is necessary to achieve the resistance to fingerprinting which characterizes the compositions of this invention.

Example 21 An ambient light-stable photosensitive imaging composition of this invention was prepared to contain:

I 500 mothyleneoxy groups per mole of combined quinones.

This composition showed good imaging speed and depth of color development upon irradiation with ultraviolet light. It is readily deactivated to a near white background on irradiation under standard conditions with 4360 A. light at 15 mw./cm. for seconds, and is substantially stable to cool white fluorescent light at a distance of 4 inches for one hour. In contrast, omitting either the pyrenequinones or the phenanthrenequinone from the above formulation results in compositions which are substantially less stable to room light; that is, they form some blue color under the above conditions.

The preceding representative examples may be varied within the scope of the present total specification disclosure, as understood and practiced by one skilled in the art, to achieve essentially the same results.

The fore oing detailed description has been given for clearness of understanding only and no unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described, for obvious modifications will occur to those skilled in the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A photosensitive composition comprising an intimate admixture of (A) a salt of a leuco triarylmethane and an acid;

(B) a hexaarylbiimidazole which absorbs principally in the ultraviolet region and is a photooxidant for the salt of the leuco triarylmethane present in an amount of from about 1 to 2 moles per mole of said salt of the leuco triarylmethane;

(C) 1,6-pyrenequinone or 1,8-pyrenequinone or both, present in an amount of from about 0.04 to 0.4 mole per mole of hexaarylbiimidazole;

(D) a visible light-absorbing carbonyl compound selected from 9,IO-phenanthrenequinone, perinaphthenone, or 4-methoxy-l,Z-naphthoquinone; present in an amount of from about 0.05 to 2 moles per mole of hexaarylbiimidazole; and

(B) an ether containing at least one oxymethylene group wherein the methylene bears at least one hydrogen; present in an amount providing from about 50 to 500 oxymethylene groups per mole of the combined quinone components (C) and (D).

2. The composition of claim 1 wherein in the leuco triarylmethane at least two of the aryl groups are phenyl groups having (a) an R R N-substituent in the position para to the bond to the methane carbon atom wherein R and R are each groups selected from hydrogen, C, to C alkyl, 2-hydroxyethyl, 2-cyanoethyl, benzyl or phenyl, and (b) a group ortho to the bond to the methane carbon atom which is selected from lower alkyl, lower alkoxy, fluorine, chlorine, bromine, or butadienylene which when joined to the phenyl group forms a naphthalene ring; and the third aryl group, when different from the first two, is selected from thienyl, furyl, oxazylyl, pyridyl, thiazolyl, indolyl, indolinyl, benzoxazoyl, quinolyl, benzothiazolyl, phenyl, naphthyl, or such aforelisted groups substituted with lower alkyl, lower alkoxy, methylenedioxy, fluoro, chloro, bromo, amino, lower alkylamino, lower dialkylamino, lower alkylthio, hydroxy, carboxy, carbonamido, lower carbalkoxy, lower alkylsulfonyl, lower alkylsulfonamido, C to C arylsulfonamido, nitro or benzylthio,

the hexaarylbiimidazole is a 2,2',4,4',5,5'-hexaphenylbiimidazole in which the phenyl groups can contain substituents having Hammette sigma values of from .4 to +4.

3. The composition of claim 1 wherein the leuco triarylmethane has the structural formula wherein R and R, are selected from lower alkyl or benzyl; Y and Y are lower alkyl; and X is selected from p-methoxyphenyl, 2-thienyl, phenyl, l-naphthyl, 2,3- dimethoxyphenyl, 3,4-methylenedioxyphenyl, or pbenzylthiophenyl;

the hexaarylbiimidazole is a 2,2',4,4',5,5'-hexaphenylbiimidazole in which the 2 and 2' phenyl rings each hear an ortho substituent selected from fluorine, chlorine, bromine, methyl or methoxy; and the 4, 4, 5 and 5' phenyl groups each are either unsubstituted or bear a lower alkoxy substituent;

the pyrenequinone present is an approximately equimolar mixture of l,6-pyrenequinone and 1,8-pyrenequinone;

the visible light-absorbing carbonyl compound is phenanthrenequinone; and

the ether has the structural formula wherein n is an integer of 0 or 1; m is an integer of 1 to 15; R is selected from hydrogen, alkyl, phenyl, alkphenyl, biphenylyl or acyl wherein alkyl, alkand acyl each contain 1 to 18 carbon atoms; and R is hydrogen when n is 0, and is hydrogen, hydroxy or OR when n is l.

4. The composition of claim 3 wherein the ether has the formula wherein m is an integer of 115; R is phenyl, alkylphenyl of 7-25 carbon atoms, or biphenylyl.

5. The composition of claim 3 wherein the hexaarylbiimidazole is present in an amount of from about 1 to 2 moles per mole of the salt of the leuco triarylmethane;

the pyrenequinone mixture is present in an amount of from about 0.1 to 0.3 mole per mole of hexaarylbiimidazole;

the 9,10-phenanthrenequinone is present in an amount of from about 0.15 to 0.75 mole per mole of hexaarylbiimidazole, and

the ether is present in an amount providing from about 50 to 500 oxymethylene groups per mole of the quinones present.

6. The composition of claim 1 wherein the leuco triarylmethane is tris(p-diethylaminoethylo-tolyl methane;

the hexaarylbiimidazole is 2,2-bis(o-chlorophenyl)- 4,4, 5,5'-tetra(m-methoxyphenyl)biimidazole;

the pyrenequinone is an approximately equimolar mixture of 1,6-pyrenequinone and Lit-pyrenequinone;

the visible light-absorbing carbonyl compound is 9,10-

phenanthrenequinone; and

the ether is an adduct of p-nonylphenol and ethylene oxide.

7. The composition of claim 1 wherein the leuco triarylmethane is a mixture of bis(p-diethyl amino-o-tolyl) (3,4-dimethoxyphenyl) methane and bis(p-diethylamino-o-tolyl) (p-chlorophenyl) methane;

the hexaarylbiimidazole is 2,2-bis(o-chlorophenyl)4,4,

5,5'-tetra(m-methoxyphenyl)biirnidazole;

the pyrenequinone is an approximately equimolar mixture of 1,6-pyrenequinone and 1,8-pyrenequinone;

the visible light-absorbing carbonyl compound is 9,10-

phenanthrenequinone; and

the etsier is an adduct of p-nonylphenol and ethylene 21 22 8. The composition of claim 1 coated on a substrate. 14. The composition of claim 1 in admixture with an 9. The composition of claim 1 coated on paper. inert solvent. 10. The composition of claim 1 coated on a synthetic References Cited A PA NTS 11. The composition of claim 1 impregnated in a sub- 5 UNITED ST TES TE Strata. 3,390,994 7/1968 Cescon.

12. The composition of claim 1 combined with a plas- 3,390,996 7/ 1968 McLachlanticizer binder matrix.

13. The composition of claim 12 in the form of a self- NORMAN TORCHIN Pnmary Examiner supporting film. 10 R. E. FICHTER, Assistant Examiner 

